Sealed batteries are well known in the art and typically include a relief/check valve for venting gases generated within the battery when the internal pressure exceeds a predetermined superatmospheric level. Nickel-zinc batteries, for example, commonly operate with a positive internal pressure of about one half pound per square inch or more to promote oxygen recombination within the battery and to keep CO.sub.2 in the air from contaminating the electrolyte when the pressure in the cell falls below zero psig. Similarly gas recombination type lead-acid batteries are known to operate at internal pressures ranging from about 1/2 psig to about 50 psig (i.e., depending on the particular application) to promote the oxygen recombination reaction and to exclude ambient oxygen from the battery. It is necessary for the prolonged life of such batteries that after the gases have been vented the relief/check valves close and reseal as near as possible to their opening pressure in order (1) to prevent unnecessary loss of the internal gases otherwise available for recombination and (2) to prevent any influx of ambient atmosphere into the battery as the internal pressure within the battery falls.
Under uncontrolled recharge, batteries can generate so much gas that the internal pressure can rapidly exceed the design pressure of the container unless the check valves are capable of quickly dumping or venting relatively large volumes (i.e., liters per minute) of the gases at relatively low internal pressures. For example, under high rate charge conditions such as can occur with a full field charge from an unregulated automobile generator/alternator or with other faulty charging equipment, some lead-acid batteries can generate more than 10 times the amount of gas otherwise generated under normal charging conditions.
Some valves commonly used in batteries do not actually reseal again until pressures as low as 25% or less of their opening pressure are reached. In fact, some such valves tested by Applicant's assignee did not reseal until the pressure in the battery had dropped below zero psig. Moreover, valves designed for rapid resealing at relatively high pressures do not usually have a capability for low pressure dumping of large volumes of gas and vice versa. No commercially available battery check valve has been found which provides both rapid, effective resealing near the opening pressure thereof as well as a high gas volume venting capability at relatively low internal pressures. In this latter regard, all of the commercial valves tested produced pressure build ups which were significantly more than twice the opening pressure of the valve in order to dump high volumes of gas.
Accordingly, it is an object of the present invention to provide a unique, compact, relief/check valve for venting an electric storage battery which valve is capable of resealing at pressures of at least about 50% or more of its opening pressure and of dumping relatively large volumes of gases under abnormal operating conditions without excessive build up of pressure within the battery container. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.